1. Field of the Invention
This invention relates generally to apparatus and methods for handling drilling waste generated in offshore drilling operations. More particularly, but not by way of limitation, this invention relates to an environmentally safe apparatus and method for slurrying waste materials and drill cuttings in a tank and transferring the waste materials and drill cuttings from the tank to other tanks or containers which is particularly suited for offshore drilling operations as well as land based operations.
2. Brief Description of the Prior Art
In the process of drilling oil and gas wells, a wellbore is drilled into the earth many thousands of feet which generates large amounts of waste material known as drill cuttings that are comprised of rock, dirt, shale and other debris. To prevent damage to the drill bit and to clear the wellbore of the drilled material, these drill cuttings are conveyed to the surface of the well bore by the drilling fluid. The waste material and drill cuttings are then separated from the drilling fluid at the surface and the drilling fluid is returned to the system and is reused while the waste material and drill cuttings are disposed of.
Because the waste material and drill cuttings contain chemicals, hydrocarbons such as oil, and other components hazardous to the environment, environmental regulations require that the waste material and drill cuttings be disposed of in an environmentally acceptable manner and prohibit disposal by dumping the materials into the sea.
Typical environmentally acceptable disposal methods include; re-injecting the waste material and drill cuttings into the earth down an injection well located at the drilling platform or at a remote location, treating the material in an accepted treatment facility usually located away from the drilling rig, or disposing of the material in a land fill location. The volume of drill cuttings generated while drilling a well bore is quite large and consists of several tons of waste material. Thus, the disposal of waste material and drill cuttings represent a major operation and expense.
Contaminated waste materials and drill cuttings recovered from an offshore drilling rig typically require removal from the rig or wellbore for treatment on land to decontaminate them before they can be disposed of safely. Because the volume of the waste material and drill cuttings can be very large, the transport of waste materials and drill cuttings from an offshore rig to a suitable decontamination facility is also a major operation.
In a conventional offshore operation, the waste material and drill cuttings are caught in small containers, known as skips, on the drilling rig, which are then lifted by a crane and loaded on a boat, transported in to a shore base facility, offloaded from the boat by a crane, dumped into a larger storage container to await processing, and then transported to a process facility. Many skips are necessary on a typical drilling rig to handle the large amount of drill cuttings generated. Dedicated crews are necessary to handle the skips on the drilling rig and at the shore base facility, cleaning crews are necessary to clean the skips after each use, safety and environmental concerns have to be addressed in each operation handling the skips. The use of skips interferes with and slows down the drilling process and creates a major environmental concern due lo the possibility of spillage. During inclement weather conditions the skips cannot be loaded on and offloaded from the boats and this, at times, stops the drilling process and increases the dangers associated with skip handling.
On offshore drilling rigs, the shale shakers and solids control equipment are permanently mounted inside enclosed structures, thus the rig has severe space limitations for the installation of additional equipment and access to the areas around the existing shale shakers and solids control equipment is limited. An offshore drilling rig also has holding tanks known as "mud pits", that are permanently installed and part of the rig sub-structure, which are used to store drilling waste and drill cuttings.
Another problem with handling waste materials and drill cuttings is that after the materials are contained in holding tanks the materials will separate into layers with the upper layer containing fluids, a lower layer containing solids, and an intermediate layer containing solids suspended in fluids. This separation also occurs in the containers or tanks that are used to transport the materials to a remote location and storage container where the materials await processing. The separation of the fluids and solids makes it difficult to remove the materials from the containers or tanks.
Angelle, U.S. Pat. No. 5,662,807 discloses an apparatus and method for handling waste comprising an elongated tank having, a longitudinal rail along a top end with a trolley mounted on the rail. An auger is mounted in the tank at one end thereof. A boom ladder is pivotally attached at an upper end to the trolley and has a pump mounted at its lower end with a shovel blade mounted outwardly of the pump. The trolley moves horizontally on the rail and the boom ladder is oscillated and pivoted from a perpendicular position to an angular position relative to the trolley by hydraulic rams. The shovel blade heaps waste in one direction to be picked up by the auger or in an opposite direction as the trolley is moved along the rail while the pump suctions off accumulated liquid. Alternatively, the boom ladder may be pivoted at an angle to place the inlet of the pump within the fluid phase level of the materials while the trolley is moved along the rail.
Angelle, U.S. Pat. No. 5,846,440 discloses an apparatus and method for handling waste comprising an elongated tank having a longitudinal rail along a top end with a trolley mounted on the rail similar to the above described '807 patent but having a vertically oriented auger mounted on the boom ladder. A boom ladder is pivotally attached at an upper end to the trolley and has a pump mounted at its lower end with a shovel blade mounted outwardly of the pump. The trolley moves horizontally on the rail and the boom ladder and attached auger is oscillated and pivoted from a perpendicular position to an angular position relative to the trolley by hydraulic rams. The shovel blade heaps waste in one direction to be picked up by the auger or in an opposite direction as the trolley is moved along the rail while the pump suctions off accumulated liquid. The pump is provided with a single slurry gate that opens or closes a secondary side inlet of the pump. The auger mounted on the boom ladder blends, mixes and disperses the solids into the fluid phase, and directs materials toward the pump. Alternatively, the boom ladder may be pivoted at an angle to place the inlet of the pump within the fluid phase level of the materials while the trolley is moved along the rail.
The apparatus and methods disclosed in U.S. Pat. Nos. 5,662,07 and 5,846,440 discussed above require a specially constructed relatively narrow tank and the pump call only be moved forward and backward and tilted at an angle relative to a vertical axis inside the narrow tank. There is no provision for sideways or lateral movement of the pump. Although the system taught by these patents may be suitable for use in land-based drilling operations, it is not particularly suited for use in offshore drilling operations. The special tank would not fit in the limited space available on a typical offshore drilling rig, the rail system cannot be fitted to conventional offshore rig fixed holding tanks, and the limited fore and aft and tilting movement of the pump would not be effective in removing materials from the conventional wider holding tanks.
The invention herein disclosed solves these problems by providing an environmentally safe apparatus and method for slurrying waste materials and drill cuttings in a tank and transferring the waste materials and drill cuttings from the tank which is particularly suited for offshore drilling operations as well as land based operations. The apparatus includes a pump having a chamber, an inlet opening into the bottom of the chamber, an impeller disposed in the chamber rotatably driven by a motor, an outlet on one side of the chamber for removal of material from the chamber into a discharge line, and circumferentially spaced circulation ports in the chamber side facing in opposed directions. The impeller extends below the chamber and breaks up debris in addition to drawing material into the pump chamber. The circulation ports may be opened or closed independently of one other, or together, to provide an exit from the chamber. The pump may be rotated by a swivel connection and moved and manipulated in the tank from end to end and top to bottom by a crane arm, or it may be suspended by cable or other means. The pump stirs up a slurry by rotating the impeller, opening the circulation ports at least partially so that the material entering the bottom inlet to the chamber and being agitated by the impeller is forced out of the circulation ports so that the material in the tank is stirred for easier pumping. The pump can operate in the stirring mode until the material to be removed is generally homogenous whereupon the circulation ports can be closed, allowing the impeller to direct the slurry through the side outlet of the chamber into the discharge line. The stirring or slurrying mode can be combined with a discharge mode by opening the circulation ports to the degree required to slurrify the material to be pumped while the material is being pumped out through the discharge line. An auxiliary discharge conduit may also be connected with the outlet to discharge material back into the tank to exchange upper fluid layers of the material with lower layers of solids and fluids and enhance the flow of the material being pumped.